Conventionally, a wind engine is classified as a horizontal axis wind engine or a vertical axis wind engine based on the orientation of rotating axes of its vanes. For vanes of the vertical axis wind engine, they are pivotably mounted in a frame. The frame is fixedly coupled to a vertical axis. Its transmission is provided near the ground. To the contrary, in the horizontal axis wind engine each vane has its horizontal axis provided above the ground by a relatively long distance. Moreover, each of a plurality of vanes of a vertical axis wind engine can adapt itself to wind by providing a wide contour in a windward condition for fully taking advantage of the force of wind and thus for generating larger torque. To the contrary, each vane can adapt itself to wind by providing a narrow contour in a leeward condition for decreasing wind friction. As an end, wind's rotation on the vanes can be maximized for rotating the wind engine. As such, many power companies have spent much time and cost in research and development of commercial wind engines which almost all are vertical axis type wind engines due to above reason.
U.S. Pat. No. 226,357 to Saccone issued on Apr. 6, 1880 discloses an early vertical axis wind engine 10 as shown in FIG. 1. The vertical axis wind engine 10 comprises a plurality of vanes 11 of flat surface each pivotably mounted near a free end of one of a plurality of arms (five are shown) 12 of a star configuration. The arms 12 are adapted to rotate in response to wind blowing over surfaces of the vanes 11. Also, the vanes 11 orbit a central, vertical axis 13. Each vane 11 can adapt itself to wind by providing a wide contour in a windward condition for fully taking advantage of the force of wind. To the contrary, each vane 11 can adapt itself to wind by providing a narrow contour in a leeward condition for decreasing wind friction. However, factors such as air dynamics and construction of the vanes 11 were not taken into consideration in the patent. As such, an abrupt operation often occurs when the wind engine 10 rotates. That is, its operation is not smooth. Further, the vanes 11 tend to cause the wind engine 10 to rotate intermittently due to centrifugal force. As such, the rotating speed of the wind engine 10 may decrease greatly. And in turn, both the arms 12 and the vertical axis 13 rotate in a speed less than wind speed.
U.S. Pat. No. 2,038,467 to Zonoski issued on Apr. 21, 1936 discloses another vertical axis wind engine 20 as shown in FIG. 2. The vertical axis wind engine 20 comprises a plurality of flat vanes 21 coupled to a rotatable frame 22. Also, each vane 21 is pivotal about a pivotal axis 211 thereof and orbits a vertical axis 23 at a center of the frame 22. The wind engine 20 is excellent in a two-phase balance. Each vane 21 is adapted to pivot about 170 degrees from windward side (i.e., having a high rotation torque) to leeward side (i.e., having a low wind friction). Ideally, a draft phase is capable of rotating more than 180 degrees per revolution of the frame 22 of the wind engine 20. However, in fact the draft phase is only able to rotate an angle less than 180 degrees due to wind shadow and interference of vanes 21. As an end, the performance of the wind engine 20 is greatly lowered.
U.S. Pat. No. 4,383,801 to Pryor issued on May 17, 1983 discloses yet another vertical axis wind engine 30 as shown in FIG. 3. The vertical axis wind engine 30 comprises a plurality of airfoils 31 pivotably mounted in a rotatable frame 32. Each airfoil 31 is designed according to the principles of air dynamics such that the frame 32 is adapted to rotate in response to wind acting on the airfoils 31. An anemoscope 34 is formed in the frame 32 via a connection to the terminal end 33 of the center shaft. An angle-of-attack of each airfoil 31 is adapted to change in response to wind direction shown by the anemoscope 34. However, such vertical axis wind engine 30 is complicated in its mechanism. The angle-of-attack of each airfoil 31 can be adjusted to an optimum only when each airfoil 31 is disposed in either upwind or leeward. As to positions other than above (e.g., side wind condition), the performance is much lowered. It is thus often that the vertical axis wind engine 30 cannot start to operate automatically even in windy weather.
U.S. Pat. No. 6,688,842 to Boatner issued on Feb. 10, 2004 discloses a vertical axis wind engine 40 as shown in FIG. 4. The wind engine 40 comprises a rotor 42 including four upper arms and four lower arms, and four airfoils 41 each pivotably mounted between two corresponding upper and lower arms of the rotor 42 by means of a pivotal axis, each airfoil 41 adapted to change its angle-of-attack in response to the force of wind acting thereon. The airfoils 41 thus pivot to cause the rotor 42 to rotate about a vertical axis 43. Further, a drive shaft in the vertical axis 43 functions as means for coupling rotational movement from the rotor 42 to an electric power generator. It is noted that in the patent each airfoil 41 is limited to pivot an angle defined by first and second stop members 441 and 442. Such stop mechanism enables each airfoil 41 to align its orientation according to wind. Further, the airfoils 41 are adapted to orbit the vertical axis 43. By configuring as above, each airfoil 41 is able to combine lift and drag in low speed into lift only when the rotor 42 is rotating at a speed the same as or even higher than the speed of wind. As an end, the force of wind can be effectively utilized for converting into rotational movement of a useful device. Thus, continuing improvements of vertical axis wind engine are constantly being sought.